1. Field of the Invention
A magnetic flowmeter for measuring the rate of flow in a liquid includes receptor means associated with the conduit, and connector means removably connected with the receptor means, said connector means containing an end-fire electromagnet for generating a magnetic flux field transversely across the conduit, and a plurality of parallel spaced sensing electrodes that extend through sealable gland passages contained in said receptor means for direct engagement at their end tips with the fluid that flows through the conduit. The electrodes are connected with flow signal processing means that include calibration factor adjustment means that are adjusted as a function of the size of the-cross-sectional area of the conduit.
2. Brief Description of the Prior Art
Flow meters for measuring the rate of flow of a fluid in a conduit are well known in the patented prior art, as shown by the Applicant""s prior U.S. Pat. Nos. 3,885,433, 4,083,246, 4,459,858 and 5,398,552.
In the known Faraday-type electromagnetic flow meters, a transverse magnetic field is established in a direction normal to the longitudinal axis of a conduit, and a pair of electrodes in contact with the fluid within the conduit are diametrically arranged along a line normal both to the magnetic field and to the longitudinal axis of the conduit, whereby the velocity of flow is measured by a meter as a function of the potential difference across the electrodes.
In the prior patent to Mannherz, U.S. Pat. No. 3,372,589, a side saddle magnetic flow meter is disclosed in which the magnetic field is produced within a relatively large pipe in a region which represents only a portion of the total cross-sectional area thereof. In order to provide an accurate reading of the flow rate through the pipe, the voltage induced in the region produces a signal that is multiplied by a factor that depends on the dimensional relationship of the region to the total cross-sectional area of the pipe. In the patent to Smoll, U.S. Pat. No. 4,195,515, a medical-type flow meter system is disclosed in which an electromagnetic assembly is removably connected by connector means with a tubular member having electrodes mounted in a common transverse plane in contact with the fluid (i.e., blood) flowing through the tabular member. By using a plurality of tubular parts in an extracorporeal circuit, measurements can be made at different points is the circuit.by moving the magnet structure part from one tubular part to another.
The Snook, et al., U.S. Pat. No. 4,346,604 discloses a medical electromagnetic flow meter having interchangeable housings and/or magnetic structures, use being made of alignment lugs that automatically effect a desired position and orientation of the lumen and electrode system relative to the magnetic structure., The reluctance of the magnetic circuit may be selectively altered by changing the position of an adjustment keeper, or a Hall probe may be provided for detecting the produced field and for increasing or decreasing the field strength to maintain predetermined values.
The aforementioned Marsh U.S. Pat. No. 4,459,858 discloses a flow meter having an electromagnetic probe which is characterized by said probe being mounted within an opening contained in the conduit for generating electrical signals as a function of the velocity of fluid flow. The probe has a debris shedding head portion which protrudes into the interior of the conduit and includes an electromagnet for generating an electromagnetic field in the fluid, the axis of the field extending normal to the direction of fluid flow. The probe further includes a plurality of electrodes arranged beyond the poles of the electromagnet and adjacent the fluid for producing the electrical signals in response to the flow of fluid through the electromagnetic field. Signal processing apparatus is connected with the sensor probe for converting the electrical signals into a flow velocity output signal. The Marsh U.S. Pat. No. 5,398,552, discloses a magnetic flow meter that has a separable magnet assembly that can be joined with a flow tube having a plurality of electrodes embedded within the flow tube. The flow tube is connected in fluid conducting relation between a pair of axially spaced sections of conduit, a first electrical connector being fixed to the outer surface of the flow tube and including first terminals electrically connected with spaced internal electrodes, respectively, that contact the fluid flowing through the tube. A second electrical connector is provided for separable connection with the first connector, which second connector includes an end-fire electromagnet for establishing a transverse magnetic field in the flow tube via the first connector, and second terminals for connecting the electrodes with a flow indicating meter via the first terminals, respectably, and a cable. In order to calibrate the meter for use with flow tubes having different internal cross-sectional dimensions, respectively, the first and second connectors are provided with cooperating size coding and decoding devices, respectively.
As distinguished from medical-type instruments for measuring the flow of blood, in the field of industrial process fluid flow such water-supply and waste-fluid removal flow measurement, the conduits are of relatively large size, and it is expensive to provide for each installation a separate flow-indicating meter that is calibrated in accordance with the size of the conduit. Furthermore, pipes or conduits of different internal dimensions have different flow characteristics, owing for example, to the high velocity of fluid flow near the center of the conduit, and a slower velocity near the wall of the conduit where the electrodes are relatively close to each other, so that the sensed velocity is not equal to the average or mean velocity of the flowing fluid. Additionally, as the fluid flows at a variety of velocities, this relationship between the sensed velocity and the mean velocity changes as a finction of fluid velocity. Therefore, for reasonable accuracy there must be an ability to establish a fixed gain multiplier for each pipe size as it relates to sensed velocity vs. mean velocity, and there must be additionally, for situations where higher accuracies are required the ability to have an addition correction factor multiplier that is a function of the velocity of the fluid.
Furthermore, the use of a probe with removable electrodes bypasses the problem of electrode fouling that could occur with the Marsh U.S. Pat. No. 5,398,552. Furthermore, having the small diameter electrodes as the only part of the assembly that must be inserted against the pressure of the contained fluid, allows for the use of the flow meter without a need for elaborate insertion hardware as in other insertible designs such as Marsh U.S. Pat. No. 4,459,858.
Accordingly, the present invention was developed to provide an improved flow-measuring system wherein a single flow-indicating meter and electrode/magnet assembly may be used to provide accurate flow measurements of fluid flow in a large number of conduits having different internal cross-sectional dimensions.
Accordingly, a primary object of the present invention is to provide an improved flowmeter including receptor means arranged on the outer circumferential surface of the conduit, and connector means removably connected with the receptor means, said connector means containing an end-fire electromagnet for establishing a magnetic field transversely across the conduit, and a plurality of parallel spaced sensing electrodes that extend through sealable gland passages contained in said receptor means, the tips of the electrodes being in direct contact with the fluids flowing in the conduit. The other ends of the electrodes are connected with flow signal processing means that include calibration factor adjustment means that are adjusted as a function of the cross-sectional area of the conduit.
Another object of the present invention is to provide an electromagnetic flow meter that is automatically calibrated for conduit size upon connection with any one of a plurality of conduits having different internal cross-sectional dimensions, respectively.
A more specific object of the invention is to provide an electromagnetic flow measuring system-including a flow tube that is connected in flow-transmitting relation between a pair of axially spaced sections of the conduit, including self-sealing glands and a second separable magnet/electrode assembly with a plurality of electrodes that can be easily inserted through the self-sealing access ports so as to make contact with the fluid contained within a pressurized flow tube, and an attached flow indicating meter for displaying the flow.
According to another object of the invention, both the flow tube and the magnet/electrode assembly are equipped with pipe size identifying means that provide for automatically calibrating the meter as a function of the internal cross-sectional dimensions of the associated flow tube. The code means may comprise spaced contacts on both the flow tube and the magnet/electrode assembly, the spacing arrangement which correspond with the cross-sectional dimensions of the flow tube, so that each spacing uniquely defines a particular flow tube size. Alternately, the code means may comprise an electronic chip embedded within the flow tube and a xe2x80x9cchip readerxe2x80x9d that is part of the magnet/electrode assembly. Other alternate means of coding are electrical terminals on one connector that are read by corresponding code-reading terminals on the other connector. Alternately, the calibration means may simply consist of a size identifying number imprinted on the flow tube where said size identifying number is manually inputted into the flow meter computing electronics via a local user interface.
According to a further object of the invention, the transverse magnetic field in the flow tube is produced by an end-fire electromagnet mounted in the magnet/electrode assembly to direct flux that is generally normal to the longitudinal axis of the conduit.
Another object of the invention is allow the flow tube self-sealing glands to be penetrated by temperature and pressure probes so that, in addition to flow, a measurement of both the pressure and the temperature of the fluid within the flow tube can be made by probes directly in contact with the fluid.